Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
  • H04L9/3263—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving certificates, e.g. public key certificate [PKC] or attribute certificate [AC]; Public key infrastructure [PKI] arrangements
  • H04L9/3268—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving certificates, e.g. public key certificate [PKC] or attribute certificate [AC]; Public key infrastructure [PKI] arrangements using certificate validation, registration, distribution or revocation, e.g. certificate revocation list [CRL]
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
  • G06F21/30—Authentication, i.e. establishing the identity or authorisation of security principals
  • G06F21/31—User authentication
  • G06F21/33—User authentication using certificates
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
  • G06Q20/00—Payment architectures, schemes or protocols
  • G06Q20/02—Payment architectures, schemes or protocols involving a neutral party, e.g. certification authority, notary or trusted third party [TTP]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
  • H04L9/3236—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials using cryptographic hash functions
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
  • H04L9/3247—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving digital signatures
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/50—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols using hash chains, e.g. blockchains or hash trees
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F2221/00—Indexing scheme relating to security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
  • G06F2221/21—Indexing scheme relating to G06F21/00 and subgroups addressing additional information or applications relating to security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
  • G06F2221/2145—Inheriting rights or properties, e.g., propagation of permissions or restrictions within a hierarchy
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L2209/00—Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
  • H04L2209/30—Compression, e.g. Merkle-Damgard construction

Definitions

• the present invention relates generally to secure communications and more particularly to schemes for certificate management.
• PKI Public Key Infrastructure
• Such certification may be provided in the form of a certificate which contains the certified data and vouches authenticity of the certified data.
• each user U chooses a signing key SK U and a matching verification key, PK,,.
• User U uses SK clause to compute a digital signature of a message m, SIGJm), while anyone knowing that PK U is U's public key can verify that SIGJm) is U's signature of m. Finding SIGJm) without knowing SK U is practically impossible.
• knowledge of PK U does not give any practical advantage in computing SK U . For this reason, it is in U's interest to keep SK U secret (so that only he can digitally sign for U) and to make PK U as public as possible (so that everyone dealing with U can verify U's digital signatures).
• PK U really is the legitimate key of user U.
• users' public keys are often "certified" by a certificate that serves as proof that U is the legitimate owner of PK U .
• the need for certification and certificate revocation extends beyond certifying public keys.
• certificates for users' public keys are produced and revoked by certifying authorities called CA's.
• a complete public key infrastructure may involved other authorities (e.g., PCAs) who may also provide similar services (e.g., they may certify the public keys of their CA's). The present discussion can be easily applied to such other authorities in a straight ⁇ forward manner.
• a CA may be a trusted agent having an already certified (or universally known) public key.
• a CA typically digitally signs PK U together with (e.g., concatenating it with) U's name, a certificate serial number, the current date (i.e., the certification or issue date), and an expiration date.
• the CA's signature of PK. is then inserted in a Directory and/or given to U himself. Note that, before certifying U's public key, it is necessary to perform additional steps, such as properly identifying user U. However, these additional steps are optional.
• SIGJM SIGJM
• a recipient R needs to obtain a certificate for PK_.
• SIGJM may be a correct digital signature of M with respect to some public key PK U , but R has no guarantee that PK chunk is indeed U's public key.
• Recipient R may obtain this certificate from the Directory, or from his own memory (if he has previously cached it), or from U himself. Having done this, R verifies (1) the correctness of the CA's certificate for PK U with respect to the CA's public key, and (2) the correctness of SIGJM) with respect to PK U . If the CA's public key is not universally known, or cached with R, then a certificate for the CA's key may also be obtained.
• a CRL may consist of the issuer's digital signature of a header comprising the issuer's name (as well as the type of his signature algorithm), the current date, the date of the last update, and the date of the next update, together with a complete list of revoked certificates (whose date has not yet expired), each with its serial number and revocation date. Since it is expected that a CA revokes many certificates, a CRL is expected to be quite long. It is envisaged that the CRL is provided to a directory who may then distribute the CRL to end users.
• the Directory After performing some checks on the CA's CRL (e.g., checking the CA's digital signature, checking that the CRL has arrived at the expected time, that a certificate declared revoked in the previous CRL of that CA - and not yet expired - still is revoked in the current CRL, etc.), the Directory stores it under its CA name.
• some checks on the CA's CRL e.g., checking the CA's digital signature, checking that the CRL has arrived at the expected time, that a certificate declared revoked in the previous CRL of that CA - and not yet expired - still is revoked in the current CRL, etc.
• the Directory When a user queries the Directory about the revocation of a certificate issued by a given CA, the Directory responds by sending to the user the latest CRL of that CA. The user can then check the CRL signature, the CRL dates (so as to receive a reasonable assurance that he is dealing with the latest one), and whether or not the certificate of interest to him belongs to it.
• each revoked certificate is specified in a CRL by means of about 9 bytes: 20 bits of serial number and 48 bits of revocation date.
• each CRL is expected to comprise thousands of certificate serial numbers and their revocation dates; the header, however, has a fixed length, consisting of just 51 bytes.
• the user may suspect that the Directory left out the certificate of interest. Indeed, even if the Directory gives the user the latest CRL of a given CA, this does not prove to the user that the certificate in question does not exist. (In fact, the actions of the Directory may actually be inte ⁇ reted as saying that the certificate is valid because it does not appear to have been revoked.) Thus in this thorny situation the Directory would have to be trusted.
• the sole figure shows a Merkle tree that is used in connection with the present invention.
• N an internal node where the left child is L and the right child is R
• V L be the value corresponding to L and V R the value corresponding to R
• V L and V R the value corresponding to R
• the value corresponding to node N must be the B-bit value H(V L V R ), where V L V R is the concatenation of V L and V R (although V L and V R may be combined by operations other than concatenation).
• Each of the values of the nodes in the authentication path is an authentication value. If most of the internal nodes of a Merkle tree have two children, it is immediately seen that an authentication path comprises roughly k authentication values where k is the depth of the tree, even though the total number of nodes can be as much as 2 . (To facilitate the verification of the value corresponding to a node N whose position within the tree is unknown, the sequence of authentication values for N can be given by specifying whether each value is a left value or a right value.
• N be the second leaf from the left in the tree T.
• V ⁇ is the value of N
• V is the value of the root
• the authentication path of N consists of the following sequence of three values: the left value V- ⁇ ,, the right value V 01 , and the right value V,.
• V ⁇ is a left value
• V 01 is a right value
• V is a right value
• a Merkle tree needs not to be a full binary tree. (For instance, if it is not, one can add dummy nodes to make it a full binary tree. Alternatively, instead of creating artificial nodes, it is possible to deem the value corresponding to any missing node a special, predetermined value, denoted by EMPTY in the sole figure.) Of course, if the tree is not sufficiently full, then authentication paths may become needlessly long.
• One way to store certificate information in a Merkle tree includes associating pieces of the certificate information to leaves of the Merkle tree. For instance, the pieces of information are the values corresponding to the leaf nodes, while the one-way hash function determines the values of internal nodes of the tree, including the root. (As discussed elsewhere herein, however, it is possible to make certificate information correspond to internal nodes, including the root.)
• certificate node Each node of the Merkle tree that corresponds to a portion of the certificate information is deemed a "certificate node".
• a simple way to associate certificate information to certificate nodes includes having as many certificate nodes as there are certificates, and making information about an individual certificate be the value corresponding to an individual certificate node.
• one or more intermediaries interact with most of the users.
• the one or more intermediaries obtain the certificate information from the CA.
• the CA may provide an intermediary with an entire authenticated tree indicating which certificates have been revoked.
• an authenticated tree is a Merkle tree (storing certificate information) having a root value that is authenticated (e.g., digitally signed) by the CA.
• the intermediary provides the user with (a) the value of certificate node N of the authenticated tree, where N is the certificate node whose value indicates that the certificate in question has been revoked; (b) the authentication path of node N in the tree; and (c) the digital signature of the CA of the root value of the tree. (Recall that this signature may include date information and additional information).
• the end user upon receiving (a), (b), and (c) from the intermediary, verifies that the digital signature of the CA is valid, thus learning the true root value of the tree. Then, the user also verifies that the authentication path for node N is valid with respect to the root value, thus learning the true information about the certificate in question. (Here by "true” we mean deemed true by the CA.)
• the user also verifies that the date information, if any, of the CA's signature of the root value is the expected date. (For instance, if the CA includes in the date information not only the date in which the authenticated tree was constructed, but also the date by which the CA intends to update the authenticated tree, the user also verifies that he is dealing with the latest authenticated tree.)
• the intermediary needs not trust the intermediary. Indeed, if the intermediary wishes to provide the user with false information about the certificate in question, the intermediary needs to perform an extraordinary amount of computation. For instance, if the intermediary wishes to modify the value corresponding to node N, the intermediary would have to either change the root value and therefore be able to forge the digital signature of the CA, or be able to break the one-way hash function.
• the amount of data that an honest intermediary provides to a user in order to allow the user to verify that the revocation information about a given certificate is authentic is not very large, especially when compared to a conventional CRL. Indeed, the bulk of the data provided to the user consists of the authentication path of the node N. For instance, if there are 3,000 revoked certificates in the tree, then certificate information about these 3,000 certificates could be associated to the leaves of a Merkle tree of depth 12. Thus, there are at most 12 values in the authentication path of node N.
• the total length of the authentication path is about 2400 bits, (more precisely, it is 11 times 200 bits for the values of internal nodes plus the length of the value of a leaf node.
• the authentication path of a certification leaf consists of one leaf value and eleven internal node values. As we shall see herein, however, even the length of leaf values can be made to be relatively small for authentication purposes.) This is much shorter than a CRL comprising the serial numbers and revocation dates of 3,000 revoked certificates.
• the new system also includes a digital signature of the root and date information, but so does the CRL system. Therefore, we succeed in a much more efficient way than a CRL system in having authentic information about certificates be provided to the end user by an intermediary without having to trust the intermediary.
• an authenticated tree is used by the CA to provide the intermediary with data enabling the intermediary to prove to end users that a given certificate of the CA has been revoked.
• the CA may also use authenticated trees so as to enable the intermediary to prove much more general certificate information. For instance, as we have said, it should be possible for an intermediary to prove to end users not only the certification status of issued certificates, but also that (alleged) certificates have never been issued by the CA. For instance, this could be done as follows: Assume that, like in the PKI envisaged in the MITRE study, a serial number consists of a twenty-bit string. Then, each possible serial number can be put in correspondence with a leaf of a full binary tree of the depth twenty.
• the CA creates and X-value such as "certificate number X has not yet been issued”, or “certificate number X (has been issued and) is currently valid", or “certificate number X has been revoked (on date dx and for reason rx)", whichever is the case.
• Each X value is then associated to a leaf of its own. Once more, in this example, certificate nodes are leaf nodes.
• the CA associates values to all other nodes of the binary tree of level twenty using a one-way hash function H so as to form a Merkle tree. Then, the CA digitally signs the root value, thus obtaining an authenticated tree.
• An intermediary can use such a tree to efficiently prove to any end user the certification status of any possible serial number for a certificate, and thus the status of any possible certificate.
• the CA may place information about certificate number X in leaf X so as to avoid having to store the serial number in the leaf.
• a leaf of a binary tree of depth twenty can be associated to a unique twenty-bit string in a natural way.
• Position information in the tree can be exploited using different ways of encoding positional information. For instance, if the serial numbers of certificates in the tree begin with number one, then certificate information for certificate serial number one can be placed in the first leaf (i.e., left most terminal leaf), certificate information about certificate serial number two can be placed in the second leaf, etc.
• an intermediary includes, but is not limited to, a directory, a distributor, a redistributor, a user, a CA, a database, a readable computer file, a read-only computer file, an entity that has obtained information from another intermediary, or any combination of the above.
• an intermediary is an entity that provides certificate information authenticated by a CA.
• a major advantage of conveying certificate information via authenticated trees consists of efficient updating. For instance, in a typical day, a CA may issue ten more certificates and revoke one previously issued certificate. In such a case, the CA may provide the intermediary with a new authenticated tree that contains the current certificate information about all certificates. More efficiently, however, the CA may provide the intermediary just with the new values of the certificate nodes, whose values have changed, together with the digital signature of the new root (and proper date information). In sum, therefore, the CA sends very little information to the intermediary. (Of course, if so wanted, teh CA can send additional information. For instance, he may send not just the certified nodes that have changed, but values of nodes that have changed and the position of these nodes. So doing, he may simplify the work of teh intermediary.)
• the intermediary could use the new received values and the old values and the one-way hash function to compute the new Merkle tree, and thus, in particular, the new root value so that the intermediary can check the digital signature of the CA and verify the new authenticated tree.
• the intermediary is now ready to provide a user with updated certificate information.
• the intermediary wishes to provide end users proofs of certificate information. For instance, a given user U may already be in possession of yesterday's entire authenticated tree. In this case, the intermediary can bring the user up to date by providing the user with just the values that have changed and the signature of the CA of the new root value. Of course, the user may not have yesterday's full authenticated tree, but he may have the full authenticated tree of, say, two weeks earlier. In this case, the intermediary may still provide the user with just the values that have changed with respect to two weeks ago along with the CA's signature of the new root value. This may still result in substantial savings.
• the intermediary may know, by keeping track of what was sent to the user, which authenticated tree the user already knows. Altematively, the user may signal to the intermediary which authenticated tree he already has and the intermediary may act accordingly. In general, the intermediary may omit sending to the user values that the user already knows. In addition, it is possible for the intermediary to obtain some of the authenticated tree information from an entity other than the CA, in which case the CA may only provide the intermediary with authenticated tree information that is not already known by the intermediary. Note that it is also possible for the intermediaries to obtain information about the tree from other sources, such as other intermediaries.
• the CA may make use of two or more Merkle trees to convey certificate information.
• a first tree may contain information about issued but non-revoked certificates
• a second tree may contain information about revoked certificates.
• the root values of these trees (together with other information deemed proper) may be digitally signed by the CA either separately or together, thus making these Merkle tree authenticated trees.
• This embodiment is similar to the two tree system described above where one authenticated tree contains infoimation about issued but non-revoked certificates and the second authenticated tree contains information about revoked certificates.
• knowing the issued certificates and revoked certificates makes it possible to determine or ascertain if a certificate is valid (i.e., by determining if the certificate is both issued and not revoked). It is also possible to construct an authenticated tree containing information about certificates that have not been issued. In that case, the authority can provide an intermediary with information for proving that one or more certificate serial numbers (or other appropriate certificate identifiers) do not correspond to any certificate that was issued as of a given date. Other possible combinations of authenticated trees containing certificate information are possible, as will become apparent from the following discussion.
• an authenticated tree may be constructed by the CA or by another entity, such as the intermediary, and that the other entity may simply present the root of the underlying Merkle tree to the CA for authentication.
• the CA it is possible for the CA to authenticate nodes, other than or in addition to the root, of a Merkle tree. In the case of a node other than the root of a Merkle tree being authenticated by the CA, an authentication path can be verified with respect to such an authenticated node rather that with respect to the root. It should be noted, however, that by authenticating (e.g., digitally signing) one or more nodes of a Merkle tree, the CA is actually generating authenticated (sub)trees that are stand- alone authenticated trees in their own right.
• certificate information CI corresponding to a certificate node N may be one-way hashed prior to being associated to the node. That is, the value associated to node N is H(CI) rather than CI.
• the process of passing from CI to H(CI) is a possible mapping step performed by a CA.
• One advantage of such a mapping is that if node N is, say, a leaf node, then whenever the value of
• N is used within an authentication path of another node, it only contributes some, say, 200 bits to such a path no matter how long CI may be. (Indeed, CI may be a very long string indicating, among other things, the reasons that a certificate has been revoked.)
• CI may be a very long string indicating, among other things, the reasons that a certificate has been revoked.
• the intermediary may not directly send data to an end user, but cause the end user to receive data (e.g., by someone else, possibly at a signal of an intermediary, or by enabling the user to read some data file, or in any other manner).
• an authenticated tree may have an underlying structure of a tree such as that disclosed in Merkle, the authenticated tree may in fact may have other interconnections and paths therethrough.
• the value of a node depend on the position, P, of the node within the tree.
• the value of the node may be H(VL, VR, P), where VL is the value of the node's left child and VR is the value of the node's right child.
• Including position information helps prevent attack by someone who attempts to find two values that hash to an actual node value of an authenticated tree.
• the node information includes position information, then a prospective attacker would have to find values that hashed to the combination of the children information and the position info ⁇ nation, which is much less likely.
• U.S. patent no. 5,432,852 to Leighton et al. discloses a similar idea used in connection with a signature scheme. Note also that the hashed value of a node could be a hash of the children concatenated with a position of the node within the tree or could be a hash of the concatenation of the children and the position.
• a CA may "Merkle" hash the quantities so as to obtain a single root- value, and then digitally signs the root-value (together with additional quantities if desired).
• This is a way to substitute n individual signatures (that can be expensive to obtain) with just one signature and n-l hashing (which are not expensive at all).
• any signature scheme can be used for the root, including pen-written signatures, rather than digital ones.
• a one-way hash function needs not to map every string to values having always B bits. For instance, it may map soem strings to 160-bit values and some other strings to 200-bit values.
• an authenticated tree needs not to be constructed by means of a single one-way hash function. For instance, a first one-way hash function could be used for nodes at the first level, a second one-way hash function for nodes at the second level, etc. More generally, one could use a different one-way hash function for each position within the tree. Notice, however, that such a collection of one-way hash functions is a single one ⁇ way hash function for purposes of constructing an authenticated tree.
• One of the prefened implementations of the various routines disclosed above is as a set of instmctions in a code module resident in the random access memory of a computer.
• the set of instructions may be stored in another computer memory, for example, in a hard disk drive, or in a removable memory such as an optical disk (for eventual use in a CD ROM) or floppy disk (for eventual use in a floppy disk drive).
• the various methods described are conveniently implemented in a general purpose computer selectively activated or reconfigured by software, one of ordinary skill in the art would also recognize that such methods may be carried out in hardware, in firmware, or in more specialized apparatus constructed to perform the required method steps.

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• 1996
  • 1996-10-11 US US08/729,619 patent/US6097811A/en not_active Expired - Lifetime
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